NEW METHOD REVEALS 15,000 YEARS OF WET SUMMERS

Using a new method to sample “hard water” deposits or coatings on buried river gravel from Wyoming’s Wind River Basin, Erik Oerter found that the interior of North America had much wetter, cooler summers during a small ice age 70,000 to 55,000 years ago, with summers 4 to 9 degrees Fahrenheit cooler than today, and winters also colder. At the time, glacial ice covered an area from the Great Lakes to the Northeast. A persistent, clockwise-rotating, high-pressure area sat over the ice sheet, pushing moist air from the Gulf of Mexico into the North American interior. Oerter defines that area rather vaguely, given the data come only from Wyoming. He says wetter summer conditions didn’t necessarily occur in Utah because it sits on the other side of the Rockies from the Wyoming study site. Oerter did the research for his doctoral dissertation at University of California, Berkeley. He now is a geology postdoctoral fellow in the U’s Global Change and Sustainability Center. His study was published Jan. 11. Oerter and colleagues determined dates, precipitation and temperature data using existing methods to analyze ratios of carbon, oxygen and uranium isotopes in the gravel coatings for the past 120,000 years. But they used new techniques with laser and ion beams to sample minute bits – one-2,500th of an inch in size – of the gravel coatings, providing a record of climate conditions on a more detailed scale of thousands of years, compared with tens of thousands previously. The coatings on the gravel are known as pedothems, soil carbonates or calcium carbonate. “They are basically hard water deposits similar to the ones on your bathroom faucet,” Oerter says.
Erik Oerter, cell: 303-990-1499, erik.oerter@utah.edu